Present day athletic (tennis) shoes, for the most part, do not provide adequate stability and protection for the foot and ankle of the wearer. This contributes to a high incidence of trauma. The currently used insole arch design provides a force which is insufficient to promote stability of the foot when the user is walking or running; and in some cases the insole arch design has been found to be actually detrimental to the protection of the foot and ankle during the more active athletic activities.
Most prior athletic (tennis) shoes become hot and uncomfortable during use since considerable heat and trauma are produced by the friction which occurs repeatedly as the feet move within the shoes. Friction is produced, for example, when the outsole of the shoe is abruptly stopped by the playing surface as inertia continues to move the foot forwardly in the shoe. Present day insoles are inefficient in preventing such forward motion of the foot, and no known lacing or design of the upper portion of the shoe can prevent the motion and resulting frictional heat.
The outsoles of prior athletic (tennis) shoes also have a common deficiency, and that is a lack of rigidity in the lateral aspect of the heel. During athletic activities, the heel of the shoe often comes into violent contact with the playing surface when the foot is in an inclined position. If the inclination of the foot is sufficient, the outside edge of the prior athletic (tennis) shoe has a tendency to collapse, so that the momentum of the body causes continued turning of the foot resulting in sprains or fractures.
The primary objective of the present invention is to provide a new insole and modified outsole for athletic shoes, and the like, by which the above-described inadequacies of the present day athletic shoes are overcome.
The insole construction of the invention, as mentioned briefly above, includes three separate pads which work together to promote greater stability of the foot within the shoe and to minimize the generation of frictional heat. These three pads consist of a tri-plane heel pad which creates a force against the plantar surface of the heel of the wearer simultaneously in all three body planes. This force prevents excessive pronation of the subtalar joint and excessive eversion of the calcaneus to enhance rear foot stability.
The prevention of excessive eversion of the calcaneus and excessive pronation of the subtalar joint also promotes forefoot stability. Forefoot instability is produced by excessive subtalar joint motion because pronation of the subtalar joint increases the total range of mid-tarsal joint motion. With the tri-plane heel pad of the present invention, stability of the forefoot is also enhanced, so that elongation of the foot is decreased, with a resulting decrease in friction and in the likelihood of sole or toe injury. Also, the use of the tri-plane pad of the invention results in the achievement of stabilization of the foot with a minimum of muscle activity, so that muscle fatigue is substantially decreased, as compared with the usual prior athletic shoe.
For a more complete discussion of the anatomy and mechanics of the foot, reference is made to "Biomechanical Examination of the Foot", Root, Orien, Weed, Clinical Biomechanics Corporation, Volume 1, published 1971, Library of Congress Catalog Card No. 71-185067.
The insole of the present invention also includes a lateral heel pad which assists the tri-plane pad in preventing eversion of the calcaneus. The force from this pad occurs primarily as the heel of the shoe meets the playing surface immediately prior to the transmission of the body weight into the tri-plane pad. The lateral heel pad also serves to reinforce the lateral heel area of the shoe.
The insole construction of the invention also includes a buttress pad which is constructed to assist in minimizing the movement of the forefoot, with a resulting minimizing in the generation of frictional heat, and a reduction in sole and toe injury. The buttress pad is located under the middle three toes in contact with the plantar (bottom surface of the toes. This increases the transmission of force into the toes producing greater propulsive stability and function of the toes. The buttress pad also provides a forward wall for the central three metatarsal heads of the foot, thus assisting in the prevention of anterior (forward) motion of the forefoot, and thereby reducing friction within the shoe and injury to the toes.
The outsole of the shoe may also be modified by the provision of inserts of relatively dense material on the medial (inside) and lateral (outside) heel area of the outsole of the shoe. The medial outsole insert is located directly below the tri-plane heel pad of the insole, and it serves to provide more efficient transmission of force into the tri-plane heel pad. The lateral outsole insert is located directly below the lateral heel pad. Its shape and location prevents collapse of the lateral area of the heel, which is a common cause of ankle injury in the use of the prior athletic (tennis) shoes.